1. Field of the Invention
The invention relates to functionalized copolymers in the form of their aqueous dispersions or water-redispersible powders, to processes for preparing them, and to their use.
2. Background Art
It is known that by using hydrolyzable vinylsilanes in the preparation of polymer dispersions, it is possible to obtain improvements in the properties as binders for paints. For instance, DE-C 2148457 (GB-A 1407827) discloses that use of aqueous dispersions comprising polymers containing copolymerized silanol groups makes it possible to enhance the wet adhesion of architectural coating compositions on a wide variety of substrates. EP-A 327376 describes the preparation of polymer dispersions based on vinyl esters, where ethylenically unsaturated alkoxysilane monomers are copolymerized by including a portion of the silane monomers in the initial charge prior to the polymerization. The polymer dispersions are recommended for preparing paints having good wet abrasion values. EP-A 327006 (U.S. Pat. No. 5,576,384) discloses low-VOC (VOC=volatile organic compounds) emulsion paints and plasters prepared using dispersions comprising copolymers containing hydrolyzable silane units. The dispersion is stabilized using hydroxyethylcellulose, nonionic emulsifier, and vinylsulfonate.
A disadvantage of the polymer dispersions known to date is that they do not bring about a general improvement in wet adhesion but instead act very differently in the various paint formulations. For instance, in a silicate-rich formulation a dispersion may have good wet abrasion resistance, whereas, if a greater amount of carbonate filler is used in the formulation, the same dispersion may lead only to paints having poor wet abrasion resistance.
An object of the invention was therefore to develop polymers which lead to coating compositions, for example, paints, which have very good wet abrasion resistance in a variety of paint formulations, for example in both silicate-rich and carbonate-rich formulations.
The invention provides functionalized copolymers in the form of their aqueous dispersions or in the form of water-redispersible powders, the copolymers comprising the reaction product of:
a) one or more monomers selected from the group consisting of vinyl esters of unbranched or branched alkylcarboxylic acids having 1 to 15 carbon atoms, methacrylic esters and acrylic esters of alcohols having 1 to 15 carbon atoms, vinyl aromatics, olefins, dienes, and vinyl halides,
b) from 0.05 to 5.0% by weight of one or more ethylenically unsaturated, hydrolyzable silicon compounds and/or hydrolyzable epoxysilanes, aminosilanes, or mercaptosilanes,
c) from 0.05 to 5.0% by weight of one or more ethylenically unsaturated epoxide monomers,
d) from 0 to 2.0% by weight of one or more ethylenically unsaturated 1,3-dicarbonyl monomers,
the figures in % by weight being based in each case on the overall weight of the monomers a) used.
Suitable vinyl esters are vinyl esters of unbranched or branched carboxylic acids having 1 to 15 carbon atoms. Preferred vinyl esters are vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate, and vinyl esters of xcex1-branched monocarboxylic acids having 5 to 11 carbon atoms, for example, VeoVa9R or VeoVa10R vinyl esters (trade names of Shell). Vinyl acetate is particularly preferred.
Suitable acrylic acid or methacrylic acid ester monomers are esters of unbranched or branched alcohols having 1 to 15 carbon atoms. Preferred methacrylic esters or acrylic esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-, iso- and tert-butyl acrylate, n-, iso- and tert-butyl methacrylate, 2-ethylhexyl acrylate, and norbornyl acrylate. Particular preference is given to methyl acrylate, methyl methacrylate, n-, iso- and tert-butyl acrylate, 2-ethylhexyl acrylate, and norbornyl acrylate.
Suitable dienes include 1,3-butadiene and isoprene. Examples of copolymerizable olefins include ethene and propene, while as vinyl aromatics, styrene and vinyl toluene may be mentioned. Examples of vinyl halides include vinyl chloride, vinylidene chloride or vinyl fluoride, preferably vinyl chloride.
The comonomers a) are preferably selected so as to give aqueous copolymer dispersions and aqueous redispersions of the copolymer powders, which, without the addition of film forming auxiliaries, have a minimum film formation temperature, MFFT, of  less than 10xc2x0 C., preferably  less than 5xc2x0 C., in particular from 0xc2x0 C. to 2xc2x0 C. The skilled worker is aware, based on the glass transition temperature, Tg, of which monomer or monomer mixtures can be used for this purpose. The Tg of the polymers may be determined conventionally, for example by means of differential scanning calorimetry (DSC). The Tg may also be approximated in advance by means of the Fox equation. According to T. G. Fox, BULL. AM. PHYSICS SOC. 1, 3, page 123 (1956), 1/Tg=x1/Tg1+x2/Tg2+ . . . +xn/Tgn, where xn is the mass fraction (% by weight/100) of the monomer n, and Tgn is the glass transition temperature, in degrees, of the homopolymer of the monomer n. Tg values for homopolymers are listed in POLYMER HANDBOOK, 2nd Edition, J. Wiley and Sons, New York (1975).
If desired, it is possible to copolymerize from 0.05 to 10% by weight, based on the overall weight of the monomers a) used, of auxiliary monomers. Examples of auxiliary monomers are ethylenically unsaturated monocarboxylic and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid, and maleic acid; ethylenically unsaturated carboxamides and carbonitriles, preferably acrylamide and acrylonitrile; monoesters and diesters of fumaric acid and maleic acid such as the diethyl and diisopropyl esters and also maleic anhydride, ethylenically unsaturated sulfonic acids and their salts, preferably vinylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid. Further examples are precrosslinking monomers such as polyethylenically unsaturated comonomers, examples being divinyl adipate, diallyl maleate, allyl methacrylate, butanediol diacrylate, and triallyl cyanurate, or postcrosslinking comonomers, examples being acrylamidoglycolic acid (AGA), methylacrylamidoglycolic acid methyl ester (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide, N-methylolallyl carbamate, alkyl ethers and esters such as the isobutoxy ethers or esters of N-methylolacrylamide, of N-methylolmethacrylamide, and of N-methylolallyl carbamate.
Preference is given to the copolymer compositions indicated below, which may further comprise the comonomer fractions b), c), and, if desired, d), and also auxiliary monomer fractions, in the stated amounts, and where the copolymer composition is chosen so that the aqueous dispersion obtainable therewith has an MFFT of  less than 10xc2x0 C., preferably  less than 5xc2x0 C., in particular from 0xc2x0 C. to 2xc2x0 C., so that there is no need for a film forming auxiliary:
vinyl ester copolymers of vinyl acetate with other vinyl esters such as vinyl laurate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl esters of an alpha-branched carboxylic acid having 5 to 11 carbon atoms, especially vinyl esters of Versatic acid having 9 or 10 carbon atoms (i.e., VeoVa9R, VeoVa10R);
vinyl ester-ethylene copolymers, such as vinyl acetate-ethylene copolymers, which, if desired, further comprise other vinyl esters such as vinyl laurate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl esters of an alpha-branched carboxylic acid having 5 to 11 carbon atoms, especially vinyl esters of Versatic acid having 9 or 10 carbon atoms or fumaric or maleic diesters;
vinyl ester-ethylene-vinyl chloride copolymers, containing as vinyl esters preferably vinyl acetate and/or vinyl propionate and/or one or more copolymerizable vinyl esters such as vinyl laurate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl esters of an alpha-branched carboxylic acid having 5 to 11 carbon atoms, especially vinyl esters of Versatic acid having 9 or 10 carbon atoms;
vinyl ester-acrylate copolymers containing vinyl acetate and/or vinyl laurate and/or vinyl esters of versatic acid and acrylic esters, especially butyl acrylate or 2-ethylhexyl acrylate, optionally further containing ethylene;
acrylate copolymers containing n-butyl acrylate and/or 2-ethylhexyl acrylate;
methyl methacrylate copolymers containing butyl acrylate and/or 2-ethylhexyl acrylate, and/or 1,3-butadiene;
styrene-1,3-butadiene copolymers and styrene-(meth)acrylate copolymers such as styrene-butyl acrylate, styrene-methyl methacrylate-butyl acrylate or styrene-2-ethylhexyl acrylate, where the butyl acrylate used may be n-, iso- or tert-butyl acrylate.
Most preference is given to vinyl ester-ethylene copolymers such as vinyl acetate-ethylene copolymers, and also to copolymers of vinyl acetate and ethylene and vinyl esters of an a-branched carboxylic acid having 9 or 10 carbon atoms (VeoVa9R, VeoVa10R), which in each case may further contain comonomer fractions b), c), and, if desired, d), and also auxiliary monomer fractions, in the stated amounts, and where the copolymer composition is chosen so that the aqueous dispersion obtainable therewith has an MFFT of  less than 10xc2x0 C.
Suitable hydrolyzable silicon compounds b) are, for example, ethylenically unsaturated silicon compounds of the general formula R1SiR0-2(OR2)1-3, where the number of R and OR2 moieties is such that the silicon is tetravalent, where R is a C1 to C3 alkyl radical, C1 to C3 alkoxy radical or halogen (e.g., Cl or Br), R1 is CH2xe2x95x90CR3xe2x80x94(CH2)0-1 or CH2xe2x95x90CR3CO2(CH2)1-3, R2 is an unbranched or branched, unsubstituted or substituted alkyl radical having 1 to 12 carbon atoms, preferably 1 to 3 carbon atoms, or is an acyl radical having 2 to 12 carbon atoms, it being possible for R2 to be interrupted, if desired, by an ether group, and R3 is H or CH3. Preference is given to gamma-acryl- and gamma-methacryloxypropyltri(alkoxy)silanes, gamma-methacryloxymethyltri(alkoxy)silanes, gamma-methacryloxypropylmethyldi(alkoxy)silanes, vinylalkyldi(alkoxy)silanes and vinyltri(alkoxy)silanes, where the alkoxy groups used may, for example, be methoxy, ethoxy, methoxyethylene, ethoxyethylene, methoxypropylene glycol ether or ethoxypropylene glycol ether radicals. Examples of suitable silicon compounds b) are vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltris-(1-methoxy)isopropoxysilane, vinyltributoxysilane, vinyltriacetoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, methacryloxymethyltrimethoxysilane, 3-methacryloxypropyltris(2-methoxyethoxy)silane, vinyltrichlorosilane, vinylmethyldichlorosilane, vinyltris(2-methoxyethoxy)silane, trisacetoxyvinylsilane, 3-(triethoxysilyl)propylsuccinic anhydride silane.
Also suitable are hydrolyzable silicon compounds from the group of the epoxysilanes and aminosilanes, such as glycidyloxypropyltrimethoxysilane, glycidyloxypropyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, and 3-(2-aminoethylamino)propylmethyldimethoxysilane.
Suitable silane compounds b) are, in particular, also mercaptosilanes of the general formula HSxe2x80x94(CR42)1-3xe2x80x94SiR53, where R4 is identical or different and is H or a C1 to C6 alkyl group, R5 is identical or different and is a C1 to C6 alkyl group or C1 to C6 alkoxy group, at least one of the radicals R5 being an alkoxy group. Preference is given to 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.
The most preferred silanes b) are vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(1-methoxy)isopropoxysilane, methacryloxypropyltris(2-methoxyethoxy)silane, 3-(triethoxysilyl)propylsuccinic anhydride-silane, 3-mercaptopropyltrimethoxysilane, glycidyloxypropyltrimethoxysilane, glycidyloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, and methacryloxymethyltrimethoxysilane, and also mixtures thereof, especially mixtures of two or more silanes from the group consisting of 3-methacryloxypropyltrimethoxysilane and methacryloxymethyltrimethoxysilane with vinyltrimethoxysilane, vinyltriethoxysilane and/or 3-mercaptopropyltrimethoxysilane and/or glycidyloxypropyltriethoxysilane. The amount of silanes b) is preferably from 0.05 to 3.5% by weight, with particular preference from 0.1 to 1% by weight, most preferably from 0.1 to 0.5% by weight, based in each case on the overall weight of the monomers a) used.
Suitable comonomers c) containing epoxide groups are glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, vinyl glycidyl ether, vinylcyclohexene oxide, limonene oxide, myrcene oxide, caryophyllene oxide, vinyltoluenes and styrenes substituted with a glycidyl radical in the aromatic moiety, and vinylbenzoates substituted with a glycidyl radical in the aromatic moiety. Preference is given to glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and vinyl glycidyl ether. The amount of epoxy compounds is from 0.1 to 5% by weight, preferably from 0.25 to 1.5% by weight, with particular preference from 0.4 to 1.2% by weight, based in each case on the overall weight of the monomers a) used. Most preference is given to copolymers comprising a combination of from 0.1 to 1.0% by weight of comonomer b) with from 0.25 to 1.5% by weight of comonomer c), in particular to combinations comprising from 0.1 to 0.5% by weight of comonomer b) with from 0.4 to 1.2% by weight of comonomer c).
In one preferred embodiment the copolymers additionally comprise monomer units of ethylenically unsaturated 1,3-dicarbonyl compounds d). Examples of polymerizable 1,3-dicarbonyl compounds are acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxyethyl methacrylate, acetoacetoxybutyl methacrylate, 2,3-di(acetoacetoxy)propyl methacrylate, and allyl acetoacetate. The preferred comonomer d) is allyl acetoacetate (xe2x80x9cacallylxe2x80x9d). The amount of 1,3-dicarbonyl compound is preferably from 0.01 to 2% by weight, with particular preference from 0.1 to 1% by weight, based in each case on the overall weight of the monomers a) used.
The dispersions are prepared by means of free radical polymerization, preferably emulsion polymerization. The polymerization is normally conducted within a temperature range from 20xc2x0 C. to 100xc2x0 C., in particular between 45xc2x0 C. and 80xc2x0 C. The initiation takes place by means of the customary free-radical initiators, used preferably in amounts of from 0.01 to 3.0% by weight, based on the overall weight of the monomers. As initiators it is preferred to use inorganic peroxides such as ammonium, sodium or potassium peroxodisulfate or hydrogen peroxide, either alone or in combination with reducing agents such as sodium sulfite, sodium bisulfite, sodium formaldehyde-sulfoxylate or ascorbic acid. It is also possible to use water-soluble organic peroxides, examples being tert-butyl hydroperoxide and cumene hydroperoxide, normally in combination with a reducing agent, or alternatively, water-soluble azo compounds. Copolymerizations with gaseous monomers such as ethylene and vinyl chloride are conducted under superatmospheric pressure, generally between 5 and 100 barabs.
To stabilize the dispersion it is possible to use anionic and nonionic emulsifiers and also protective colloids. Preference is given to using nonionic or anionic emulsifiers, preferably a mixture of nonionic and anionic emulsifiers. As nonionic emulsifiers it is preferred to use condensation products of ethylene oxide or propylene oxide with linear or branched alcohols having 8 to 18 carbon atoms, alkylphenols or linear or branched carboxylic acids of 8 to 18 carbon atoms, and also block copolymers of ethylene oxide and propylene oxide. Examples of suitable anionic emulsifiers are alkyl sulfates, alkylsulfonates, alkylaryl sulfates, and also sulfates or phosphates of condensation products of ethylene oxide with linear or branched alkyl alcohols containing from 5 to 25 EO units, alkylphenols and monoesters or diesters of sulfosuccinic acid. The amount of emulsifier is from 0.5 to 10% by weight, based on the overall weight of the monomers a) used.
If desired, it is also possible to use protective colloids. Examples of suitable protective colloids are polyvinyl alcohols containing from 75 to 95 mol %, preferably from 84 to 92 mol %, of vinyl alcohol units; poly-N-vinylamides such as polyvinylpyrrolidones; polysaccharides such as starches, and also celluloses and their carboxymethyl, methyl, hydroxyethyl, and hydroxypropyl derivatives; synthetic polymers such as poly(meth)acrylic acid, and poly(meth)acrylamide. Particular preference is given to using the abovementioned polyvinyl alcohols. The protective colloids are generally used in an amount of from 0.5 to 10% by weight, based on the overall weight of the monomers a) used.
If desired, the molecular weight may be controlled using the customary regulators or chain transfer agents, examples being alcohols such as isopropanol, aldehydes such as acetaldehyde, chlorine compounds, mercaptans such as n-dodecyl mercaptan and t-dodecyl mercaptan, and mercaptopropionic acid (esters). In the preparation of the dispersion, the pH may be adjusted using pH regulator compounds such as sodium acetate or formic acid.
The polymerization may be conducted, independently of the particular polymerization process, with or without the use of seed lattices, with the inclusion of all or one or more individual constituents of the reaction mixture in the initial charge, or with the inclusion of some of the constituents, or some of the individual constituents, in the initial charge and the subsequent metered addition of the remainder of the constituents of the reaction mixture, or by the metering technique without an initial charge. In order to prepare the dispersion, the comonomers a), b), c), and, if desired, d) may all be included in the initial charge (batch process) or else a portion of the monomers is included in the initial charge and the remainder is metered in (semibatch process).
Preferably, all of the silane fraction b) is metered in during the polymerization and the epoxide fraction c) is metered in likewise. With particular preference, the epoxide fraction c) is metered in toward the end of the polymerization, at a conversion between 80 to 100%. All or some of the 1,3-dicarbonyl compound d) may be metered in, or it may be included in its entirety in the initial charge. Preferably, all or a portion of the 1,3-dicarbonyl compound d) is metered in during the polymerization, and with particular preference, all. In a further preferred embodiment, two or more different silanes are metered in during the polymerization. For example, first one or more silanes are metered in continuously and another, different silane is metered in together with the epoxide fraction after the end of the metering of the first silane or silanes. The emulsifiers and/or protective colloids used to stabilize the dispersion may all be included in the initial charge, or some may be included in the initial charge while the remainder is metered in during the polymerization. In this context, the surface-active substances may be metered in on their own or in the form of a preprepared emulsion with the comonomers.
After the end of the polymerization, post polymerization may be carried out using known methods in order to remove residual monomers, an example of such a method being post polymerization initiated with a redox catalyst. Volatile residual monomers and other volatile, nonaqueous constituents of the dispersion may be removed by means of distillation, preferably under reduced pressure, optionally by stripping with inert entraining gases such as air, nitrogen or water vapor through or over the dispersion.
The aqueous dispersions obtainable with the process of the invention have a solids content of from 40 to 70% by weight, preferably from 50 to 65% by weight. To prepare water-redispersible polymer powders, the aqueous dispersions, following the optional addition of protective colloids as a spraying aid, are dried, for example by means of fluidized bed drying, freeze drying, or spray drying. Preferably, the dispersions are spray-dried. Spray drying takes place in standard spray-drying units, in which atomization may take place by means of one-fluid, two-fluid or multifluid nozzles, or with a rotating disk. The chosen exit temperature is generally in the range from 45xc2x0 C. to 120xc2x0 C., preferably from 60xc2x0 C. to 90xc2x0 C., depending on the unit, on the Tg of the resin, and on the desired degree of drying.
In general, a spraying aid, when utilized, is incorporated in a total amount of from 3 to 30% by weight based on the polymeric constituents of the dispersion. Suitable spraying aids are the protective colloids already mentioned. In the course of spraying, the presence of up to 1.5% by weight of antifoam, based on the base polymer, has proven favorable in many cases. In order to improve the blocking stability, the powder obtained may be provided with an antiblocking agent (anticaking agent), preferably up to 30% by weight, based on the overall weight of polymeric constituents. Examples of antiblocking agents are Ca or Mg carbonate, talc, gypsum, silica, kaolins, and silicates.
The procedure of the invention makes it possible to obtain copolymers which, in both silicate-rich and carbonate-rich paint formulations, lead to coatings having high wet abrasion resistance. With the binders known to date, based on silanol-functional copolymers, satisfactory wet abrasion resistance was possible only in paint formulations containing silicate-rich filler fractions.
The functionalized copolymers in the form of their aqueous dispersions and water-redispersible powders are suitable for use in adhesives and coating compositions, especially in the building sector, in tile adhesives and exterior insulation system adhesives, and especially for use in low-emission polymer emulsion paints and polymer dispersion plasters. The formulations for emulsion paints and dispersion plasters are known to the skilled worker, and generally contain from 5 to 50% by weight of functionalized copolymer, from 5 to 35% by weight of water, from 5 to 80% by weight of filler, from 5 to 30% by weight of pigments, and from 0.1 to 10% by weight of further additives, the figures in % by weight in the formulation adding up to 100% by weight.
Examples of fillers which can be used are carbonates such as calcium carbonate in the form of dolomite, calcite, and chalk. Further examples are silicates, such as magnesium silicate in the form of talc, or aluminum silicates such as loam or clay; quartz flour, quartz sand, highly disperse silica, feldspar, heavy spar, and light spar. Fibrous fillers are also suitable. In practice, mixtures of different fillers are used in many cases, examples being mixtures of fillers of different particle size or mixtures of carbonate and silicate fillers. In the latter case, with carbonate or silicate accounting for more than 50% by weight, in particular more than 75% by weight, of the overall filler fraction, the formulations are referred to as carbonate-rich or silicate-rich, respectively. Polymer plasters generally comprise coarser fillers than do emulsion paints. The particle size in this case is often between 0.2 and 5.0 mm. Otherwise, polymer plasters may comprise the same additives as emulsion paints.
Examples of suitable pigments, in a non-limiting sense, are titanium dioxide, zinc oxide, iron oxides, and carbon black, as inorganic pigments, and also the customary organic pigments. Examples of further additives are wetting agents in fractions of in general from 0.1 to 0.5% by weight, based on the overall weight of the formulation. Examples thereof are sodium and potassium polyphosphates, polyacrylic acids, and salts thereof. Further additives worth mentioning are thickeners, used generally in an amount of from 0.01 to 2.0% by weight, based on the overall weight of the formulation. Customary thickeners are cellulose ethers, starches, or bentonite as an example of an inorganic thickener. Further additives are preservatives, defoamers, and antifreeze agents.
To prepare the adhesives and coating compositions, the polymer dispersion or polymer powder is mixed and homogenized with the other formulating constituents, filler and further adjuvants, in appropriate mixers. If desired, the polymer powder may also be added in the form of an aqueous redispersion on the building site. In many cases, a dry mix is prepared and the water required for processing is added immediately before processing. In the case of the preparation of pastelike compositions, it is common to introduce the water fraction first, to add the dispersion, and finally to stir in the solids.
In the context of their use in coating compositions, a particular feature of the functionalized copolymers is that they still guarantee high wet abrasion resistance even at a high pigment volume concentration (PVC), i.e., in highly filled and supercritically formulated compositions (PVC greater than 65%). In general, the PVC is xe2x89xa750%, preferably from 60 to 85%, and is calculated by PVC (%)=(Vp+fxc3x97100)/(Vp+f+Vb), where Vp+f=volume of pigment+filler, and Vb=volume of binder. The functionalized copolymers are particularly advantageous as binders in coating formulations for low-emission interior paints, especially those with a high PVC. (highly filled paints).
The examples below serve to illustrate the invention.